1. Field of the Invention
The present invention relates to an output voltage stabilizing circuit of a power factor correction circuit, and more particularly to an output voltage stabilizing circuit of a power factor correction circuit which, at an initial power-on stage, stabilizes an output voltage of the power factor correction circuit by controlling an on/off timing of a reference oscillating waveform which varies in response to an error voltage in accordance with a charge/discharge voltage outputted from a soft start circuit section.
2. Description of the Prior Art
Generally, industrial or household electric appliances use a direct current (DC) power supply as its operating power supply. The DC power supply is generally produced by a circuit rectifying a commercial alternating current (AC) power supply, such as a capacitor-input type rectifying circuit which has a simple circuit construction. However, the capacitor-input type rectifying circuit has a low power factor because the input current has a pulse type of flowing only over the peak part of the input AC voltage. For this reason, electric appliances generally employ a power factor correction circuit.
FIG. 1 shows a power supply circuit of an electric appliance employing a conventional power factor correction circuit.
Referring to FIG. 1, the power supply circuit of an electric appliance employing a conventional power factor correction circuit including a rectifying section 1 for rectifying a full wave of an input AC power supply; a power factor control section 2 for controlling a power factor or the power supply voltage which has been rectified by the rectifying section 1; a switching mode power supply (SMFS) circuit section 3 for switching a power supply voltage having a power factor corrected by the power factor control section 2 and supplying the switched power supply voltage to a load terminal of the electric appliance; and a digital pulse modulation (DPM) control circuit section 4 for controlling operation of the power supply voltage of the SMPS circuit section 3 in response to a DPM power conservation mode.
The power factor control section 2 is connected to an output terminal of the rectifying section 1 by a coil L1. A diode D1 is connected between one end of the coil L1 and the input terminal of the SMPS circuit section 3. A field effect transistor (FET) Q1 is connected between the coil L1 and the diode D1. A power factor correction control circuit section 2a is connected to a gate terminal of the FET Q1, and a capacitor Cl is connected between one end of the diode D1 and one end of the FET Q1.
The power supply circuit comprising the conventional power factor correction circuit is operated as follows.
If an AC power supply is inputted to the rectifying section 1, the rectifying section 1 full-wave-rectifies the AC current power supply, and inputs the rectified power supply into the SMPS circuit section 3 via the coil L1, diode D1 and the capacitor C1. Then, the SMPS circuit section 3 voltage-converts the inputted power supply voltage to supply the converted power supply voltage to the load terminal. The power factor of the power supply voltage is controlled by the power factor correction control circuit section 2a. For instance, if the power supply voltage inputted to the SMPS circuit section 3 is logic high, the power factor correction control circuit section 2a turns on the FET Q1, thereby lowering the power supply voltage. If the power supply voltage becomes logic low to a certain level by operation of the FET Q1, the power factor correction control circuit section 2a turns off the FET Q1.
The power factor of the power supply voltage inputted to the SMPS circuit section 3 can be corrected by undergoing the above process. In a DPM normal mode described above, the DPM control circuit section 4 outputs a logic high signal to the SMPS circuit section 3, and the SMPS circuit section 3 is operated in a DPM normal mode, thereby supplying a full electric power to the load terminal. In a DPM-off mode, the DPM control circuit section 4 inputs a logic low signal to the SMPS circuit section 3 to operate in a conservation mode. The SMPS circuit section 3 then does not supply the power supply voltage to the load terminal, thereby minimizing consumption or the electric power.
However, the power supply circuit of an electric appliance comprising the conventional power factor correction circuit described above has a drawback that the SMPS circuit section 3 operates a voltage conversion before the power factor control section 2 stabilizes the power factor of the output voltage. This drawback makes the output voltage of the power factor control section 2 very unstable.